(1) Field of the Invention
The present invention generally relates to a pulsed arc welding apparatus, and more particularly to a pulsed arc welding apparatus having a consumable electrode wire wherein a workpiece is welded with the electrode wire located within a shield gas, by supplying a pulsed arc welding current to the electrode wire.
(2) Description of the Related Art
It is known that when a pulsed arc welding is performed to weld a workpiece by using a consumable welding wire an electromagnetic arc force due to the arc current is applied to the workpiece.
If the workpiece has portions with various thicknesses to be welded, it is likely that a thin portion of the workpiece may completely melt by the heat of arc at the end of the wire through the pulsed arc welding and become undesirably perforated at the weld portion. In order to eliminate this problem, it is necessary to reduce the electromagnetic arc force. In the case of a conventional pulsed arc welding apparatus, the peak current or the duty ratio of a peak pulse time within a total duty-cycle time for a thin portion of the workpiece is reduced to a smaller value than a value of the peak current or the duty ratio of a peak pulse time within a total duty-cycle time for a thick portion of the workpiece.
However, in the conventional pulsed arc welding apparatus, the peak current must be preset prior to the start of the welding operation. It is known that the arc discharged between the wire and the workpiece will become unstable as the peak current is changed to a smaller value. The arc length between the wire and the workpiece will not be stabilized if the discharged arc becomes unstable. If the arc length is not stable, it is likely that undesired spatter and weld-bead problems may be produced by the conventional pulsed arc welding apparatus.
For these reasons, in the conventional pulsed arc welding apparatus, the peak current is preset to a relatively great value, and the duty ratio of a peak pulse within a total duty-cycle time is predetermined so as to control the arc force appropriate for a weld portion.
However, when the welding of a workpiece having portions with various thicknesses is performed, it is likely that undesired spatters and weld bead problems appear. If the duty cycle is reduced to a smaller value at the time of the welding of a thin portion of the workpiece, the average current needed to discharge the arc between the wire and the workpiece cannot be maintained at a desired current. It is difficult, with the conventional pulsed arc welding apparatus, to transfer a droplet from the welding wire to the workpiece for one pulse at an appropriate rate. As a result, an adequate thickness for a weld joint may not be obtained and the mechanical strength of the resulting weld joint may be deteriorated.